Subseafloor Ocean Crust Microbial Observatories: Development of FLOCS (FLow-through Osmo Colonization System) and Evaluation of Borehole Construction Materials

Although oceanic crust is the largest contiguous, hydrologically active environment on Earth, very little is empirically known about crustal habitability due to obstacles faced in scientific sampling, especially in basaltic crust. Geologically young, chemically reduced basaltic crust is not in thermodynamic equilibrium with seawater or hydrothermal fluids; exploitation of the inherent thermodynamic disequilibrium may fuel microbial ecosystems in subsurface environments. One avenue to explore the basaltic deep biosphere is through the deployment of microbial observatories at seafloor exposures and inside boreholes drilled into the crust. We report the design and field-testing of flow-through microbial observatories for use in deep biosphere studies conducted in boreholes within oceanic crust. We also evaluate the suitability of borehole construction materials in order to inform the development of the next generation of observatories for microbial studies, with attention towards minimizing in situ leaching of (potentially) growth-inducing substrates (i.e., carbon, nitrogen, iron).